Northern Ireland's deputy first minister, Martin McGuinness, has warned dissident republicans that any violence during the G8 summit would backfire on them.

Sinn Féin's chief negotiator during the peace process said on Wednesday said the new IRA, Continuity IRA and Óglaigh na hÉireann would be defying the will of the people, including those out protesting this weekend against world hunger, corporation tax evasion and war, if they committed violent acts.

Addressing republican dissidents, McGuinness said: "To people who are from here who might think that this is an opportunity to exploit [the G8] for their own interests, I believe they would be making a huge mistake because they run the very great risk of being confronted by peaceful protesters who want absolutely nothing to do with any violence or conflict on the streets."

He also urged anarchists and radical anti-capitalist groups to stay away from mainstream protests by the trade unions, churches and charities being staged in Belfast on Saturday and Enniskillen on Monday.

"I think all the people who come here from other parts of the world need to be very conscious that they are coming to a place that is no longer at conflict, to a country at peace. I would like them to respect our peace when they come.

"We certainly respect their right to come and articulate their views around issues that I feel equally strongly about such as world conflict, hunger, poverty, unfair taxation," McGuinness said.

More than 7,000 police officers are being deployed in the biggest ever security operation in Northern Ireland. To cope with potential street disorder extra cells have opened in the top security Maghaberry prison and late night courts could be also be held from Saturday onwards to process offenders.

McGuinness's message to the three republican terror groups opposed to the peace process is unlikely to influence any plans they may have for the G8, when up to 2,000 journalists from around the world will be present.

The security forces north and south of the Irish border believe the dissidents are unlikely to strike in a heavily fortified and policed Fermanagh. Instead, they are bracing themselves for attacks in other parts of Northern Ireland in the buildup and during the G8 summit.

In the Irish Republic the Garda Síochána have made several arrests over the last 48 hours as part of a security crackdown on republican dissidents.

Gardai said a 49-year-old man and a 43-year-old woman were arrested at Castlebellingham in County Louth on Monday.

A short time later, a man aged 30 was arrested in Navan, Co Meath.

A spokesman said a fourth person, a 38-year-old man, was also detained in Navan on Tuesday.

The men are being held under section 30 of the republic's Offences Against the State Act at separate garda stations while the woman has been released.

"As part of the operation a commercial premises in Navan was searched along with three residences in Drogheda, Navan and Castlebellingham."